Wilson Alexia 2 lacking some bass

I also have the Alexia 2's.  I run it with Esoteric electronics.  The Alexia's bass is awesome is the word that comes to mind.  It's the sitting position that is the problem.  I found moving the sitting a couple of feet closer or further away from the speakers are areas of bass nulls.  Try it, move around your sitting position and see for yourself.

Suggest you try a good preamplifier in your system. My Bartok sounds great until I put the Conrad-Johnson ART88 pre back in the system. A much fuller more complete sound stage. Most, including now even Paul McGowan who fought the concept of a preamplifier, seem to find a more complete presentation with a pre in the system.

You may be sitting in a null. I had a room 15 x 20 x 8 and needed to move my seat back until the room response flattened out from my ear position. I did this 6 inches at a time with the laptop and mic until it was optimized. It was not at the 62% back rule of thumb. Roughly your 15 ft has a resonant freq of 37 hz and your 8 ft ceiling is 70. That is a problem right away. Your 20 feet is about 28 hz. That room had Sasha One's.

Today's room has Alexia One's. I had to bass trap the heck out of it to make it flatter. See my virtual room in Tennessee. The Sasha room is also in the system under Kentucky.

I think this is readily solvable. Your gear is stellar.

Set your speakers for best imaging get some Rel 812's

I have had Alexia 2s and now Alexia Vs. I agree with others here. The lack of bass is usually caused by the location in the room. One of the key factors is whether the port is reinforced by the wall behind the speakers. Move them closer to the wall and see what happens. You should be able to attain excellent bass with your system. Don't change your amps.